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60 generations of selection for an index combining high body weight and high stress resistance in laboratory mice.

Abstract

A modified exponential model was used to analyse the direct response of long term selection among full-sib-families (2 test-males per litter, 80 pairs per line and generation , selection proportionaboil 50%) in outbred laboratory mice. The selection criterion was an index combining the genetically negatively correlated traits: high body weight (BW) and high stress resistance. To quantify the stress resistance the treadmill performance (TP) was measured as the distance to exhaustion Starting at 7545 index units (IU) in generation 0 the index came up to 118580 IU in generation 60. That « a total selection response of 4313 IU or about 57%, equivalent to 12 Sp or 21 Sg. The realised hentability for the index converted to an individual base was initially 0.33, decreasing to 0.03 at generation 60. The half live was 24 generations. . _ . Selection response in the index line (DU-6+LB) was compared to the devebpmerrt of stress resistance in 3 lines, 2 were single trait selected for growth traits (body weight - line DU-6) protein amount - DU-6P) and the control ( DU-Ks). Means for treadmill performance in generation 50 in lines DU-Ks^ DU-6 DU-6P DU-6+LB were estimated as 2000m (100%), 272m (14%), 441m (22/o) and 2853 m (143%), respectively. Body weights were 28.7g (100%), 54.6g (190%), 4 9 19 (60%). These results demonstrate the combining possibility of high growth and high TP and the negative effects of single trait selection for growth traits on TP.